In certain situations, free radicals can be generated in an exaggerated manner and can injure tissues and organs by interacting with lipids, proteins, or DNA. So, oxidative stress has been implicated in a large number of human diseases. To survive, the human body has developed a complex, efficient, and highly adaptive antioxidant defense system. The eye is also protected against oxidative stress by several mechanisms involving antioxidant enzymes such as catalase (CAT) and superoxide dismutase (SOD), as well as by low-molecular-weight antioxidants such as glutathion (GSH) and ascorbate.